Argument: Iron-fertilized algae blooms can deplete marine oxygen levels
"A scientific critique of oceanic iron fertilization as a climate change mitigation strategy". Greenpeace Research Laboratories. September 2007 - "Iron addition and subsequent phytoplankton blooms, associated with increased particulate organic export and remineralization, could reduce oxygen levels in subsurface waters. Low oxygen levels would lead to a negative impact on many marine organisms because they need oxygen to breathe. Indeed, an early modelling study of large-scale iron fertilization predicted that it would lead to significant deep ocean oxygen depletion in one region of the oceans studied."